1. Field of the Invention
The present invention relates generally a hardware based scrubbing implementation for use in physical layer controllers used in data transmission networks.
2. Discussion of the Prior Art
One type of high speed data transmission network is defined by the Fiber Distributed Data Interface (FDDI) protocol. The FDDI protocol is an American National Standards Institute (ANSI) data transmission standard which applies to a 100 Mbit/second token ring network that utilizes an optical fiber transmission medium. The FDDI protocol is intended as a high performance interconnection between a number of computers as well as between the computers and their associated mass storage subsystem(s) and other peripheral equipment. Information is transmitted on an FDDI ring in frames that consist of 5-bit characters or "symbols", each symbol representing 4 data bits. Tokens are used to signify the right to transmit data between stations. The FDDI Station Management (SMT) standard provides the necessary control of an FDDI station (node) so that the node may work cooperatively as a part of an FDDI network.
To effectively implement the functions required, SMT is divided into three entities, namely the Connection Management entity (CMT), the Ring Management entity (RMT) and the Frame Based Services. The Connection Management (CMT) is the management entity in the Station Management that is responsible for the node's port(s), as well as the connection to the ports of neighboring nodes.
The Connection Management is further divided into three sub-entities. They include, the Physical Connection Management (PCM), Configuration Management (CFM) and Entity Coordination Management (ECM). The CFM is responsible for defining the interconnections of the ports and MAC(s) within a node. Thus the CFM controls the routing of data within the node. In hardware implementations, the routing through each resource is controlled by programming a configuration switch. A general description of the Station Management standard, as well as each of its subparts, including the Connection Management (CMT), the Configuration Management (CFM) and the Physical Connection Management (PCM) is described in detail in the draft ANSI FDDI Station Management Standard, dated Jun. 25, 1992, which is incorporated herein by reference.
The members of an FDDI network generally fall into the classifications of single attachment nodes and dual attachment nodes. Dual attachment nodes have two ports to accommodate the dual trunk tings of the FDDI network. Single attachment stations have a single port and therefore cannot directly attach to the dual trunk tings. Rather, the single attach stations typically are coupled to the trunk rings through a concentrator that forms the root of a tree. The concentrator may be single attachment or a dual attachment type. Thus, a typical FDDI network may consist of a plurality of dual attachment nodes arranged in a trunk ting. The dual attachment nodes may include both dual attachment stations and dual attachment concentrators. Each dual attachment concentrators forms the root of a concentrator tree. The concentrator tree may include various concentrators that form the root of tree branches and stations. As used hereafter, the terms "node" and "station" are intended to be generic and apply to both formal FDDI stations and FDDI concentrators.
Each dual attachment node contains two Ports designated as A and B. Port A is intended to be connected to the primary ring on the incoming fiber and the secondary ring on the outgoing fiber. Similarly, Port B is intended to be connected to the incoming fiber of the secondary ring and the outgoing fiber of the primary ting. Therefore a properly formed trunk ring is composed of a set of stations with the Port A of one station being connected to the port B of the neighboring station.
Concentrator nodes contain one or more Ports of type M to provide connections within a concentrator tree. A single attachment node (whether it be a station or concentrator) has an S type Port which is intended to be attached to an M type port within a concentrator tree. Accordingly, a standard FDDI network would typically have as many as four different types of ports. That is, A, B, M, & S type ports. Each of these port types requires a physical layer controller.
The FDDI SMT standard contemplates that there are numerous internal configurations that an FDDI node must be able to support. For example, any given port may be isolated. That is, not connected to any other internal ports or MACs. In this situation data received through an input line P.sub.in would be passed directly out of the node through the output line P.sub.out of the same port. Alternatively, a port may route received data through only one of a primary internal path, a secondary internal path or a local internal path that are located within the node. In such cases, after passing through the selected internal data transmission path, the data may be outputted from the node through either the same port or a different port, depending upon the circumstances. For example, when a loop test is being conducted, it is common to output the data through the same port that it is received by.
The standard active FDDI configuration for a dual attach station is a thru configuration wherein the network's primary data transmission path enters the A port, passes through the nodes internal primary path and emerges from the B port. At the same time the network's secondary data transmission path enters the B port, passes through the nodes internal secondary path and exits through the A port. The internal paths may require the data to physically pass through any number of (or no) MACs. Alternatively, the port may be connected in a concatenated arrangement wherein after entering through the input line P.sub.in of a particular port, the data path passes through both the primary and secondary internal data paths within the node before exiting the output line P.sub.out of the same port. In a dual attach station, this arrangement is particularly likely in the event of a failure in the second port or a failure in the connection between the second port and its neighbor. The internal configurations that are permissible in accordance with the FDDI standards are set forth in detail in the above referenced SMT standard.
As is well known to those familiar with FDDI data transmission networks, a station or concentrator (node) that is to form an active part of an FDDI network must be capable of reconfiguring itself in the event of a failure in the network. When such a failure occurs, it is often difficult to determine whether the information currently on the ring is consistent or not as well. Therefore, the FDDI standards call for erasing information that is on the ring when a fault occurs if there is a possibility that the information can be isolated from the media access controller (MAC) that sourced the information. This is referred to as scrubbing.
If scrubbing is controlled through software intervention, then the reconfiguration process is slowed unnecessarily. On the other hand, if all of the outputs are scrubbed, data transmission paths that are not affected by the reconfiguration would be broken unnecessarily for a period of time, thereby reducing the network performance.